<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>05_版心与居中测试</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        .main{

        }
    </style>
</head>
<body>
    <div class="main">
        <div class="center">
            <div class="card">我是内容</div>
            <div class="card">我是内容</div>
            <div class="card">我是内容</div>
        </div>
    </div>
</body>
</html>